Wallaces Farmer

Soil temperature at planting time is a key factor in determining corn stand establishment.

Rod Swoboda 1, Editor, Wallaces Farmer

April 13, 2016

5 Min Read

Ideal planting conditions are when the soil temperature reaches 50 degrees F and is expected to continue warming, says Mark Licht, Iowa State University Extension cropping systems agronomist. This temperature is a key factor to getting corn seed to germinate and emerge within seven to 10 days (90-120 growing degree units).

The first step in getting a uniform stand of corn is to have the corn planter properly maintained and adjusted. You want to plant the corn crop as uniformly as possible. The next step in the uniformity equation is achieving uniform corn emergence.


“Germination is simply the process that allows a seed to sprout or begin to grow,” explains Shane Brockhoff, an agronomist for AgriGold in western Iowa. “Although the definition is simple, the actual process is quite complex. The germination of a corn seed requires soil moisture to ‘reawaken’ the seed and adequate temperatures to speed along the enzymes and chemical reactions that allow the cells in the corn plant to grow and reproduce.”

What determines success or failure of corn germination?

Corn growers know the importance of germination but often don’t believe they have much of a role in that process. Growers tend to be disconnected from the germination process because they cannot control the rainfall, sunshine and/or temperatures. But where and how a grower places the corn seed in the ground greatly dictates the ultimate success and/or failure of germination, he notes. The success of germination is achieved by providing the corn seed with:

1) adequate and uniform moisture;

2) adequate and uniform soil temperature; and

3) adequate and uniform soil-to-seed contact.

Pay close attention to the fact that no values are assigned to these requirements. Brockhoff says that’s because germination can occur at various temperatures and soil moisture conditions, but the corn grower’s goal is to achieve uniformity. Research continues to show that once a corn seed spikes through the soil, all its neighbors need to spike through within a 48 hour window, to keep the plant from becoming a weed. That is, to keep it from competing with its neighboring plants for sunlight and moisture.

Therefore, if emergence conditions are uniform (not necessarily perfect) the chance of having a uniform germination of the seed and ultimately a uniform emergence of the corn plants is greatly improved.

How do the three requirements impact the germination process? Brockhoff provides the following explanation.

Adequate and uniform moisture in the seed zone: Corn kernels must absorb water equaling about 30%

of their weight before germination can begin. So there must be enough water present in the soil. Too little water stalls the process while too much water can lead to premature death by rotting. Uniformity of soil moisture is necessary so all seeds have the same access to water.

Adequate soil moisture begins with uniform planting depths greater than 1½ inch to avoid uneven soil moistures caused mainly by tillage patterns through the field. The other consideration with moisture absorption is the temperature of the water that is absorbed. A majority of the water is absorbed into the corn seed within the first 36 hours. If the first “drink” of water is extremely cold, it causes the seed to go into shock and disrupts the emergence process. Thus, to aid in uniform emergence you need to ensure the soil water that the seed is absorbing is above the 50 degree F level.

Adequate and uniform soil temperature in seed zone: Adequate soil temperature is defined as being greater than 50 degrees at the 2-inch depth. Soil temperatures need to be above 50 degrees for corn to germinate uniformly and quickly. Any temperature below 50 degrees will slow the process and cause germination to be variable, resulting in loss of yield.

Once again a planting depth greater than 1½ inches may lead to lower soil temperatures compared to shallower planting, but the temps will be more uniform, which is the goal. Potential causes for variability in soil temperatures in the seed zone include different soil types and uneven crop residue distribution, but most often it is caused by uneven planting depth.

Adequate and uniform soil-to-seed contact: In order for corn kernels to absorb moisture quickly and uniformly, the soil must be firmly packed around the kernel. Any time there is an air pocket around the seed, moisture uptake is slowed and ultimately the germination process is severely hampered. To achieve adequate soil-to-seed contact, you need to ensure the double disk openers create a “V” shaped trench, the closing wheels system is centered over the row and there is adequate down force to gently pack the soil around the seed.

Obstacles to getting adequate soil-to-seed contact include cloddy fields caused by working soils too wet, open planting furrows caused by planting in soils too wet or by too much crop residue being present in the planter furrow.

“Uniform germination leads to uniform emergence that leads to uniform plants and ultimately high yield potential,” says Brockhoff. “When looking at the success of the planting operation, if the germination appears to be less than desired, you should begin looking at the three fundamentals of germination to determine what can be fixed for future success.” For more agronomic information, visit agrigold.com.

About the Author(s)

Rod Swoboda 1

Editor, Wallaces Farmer

Rod, who has been a member of the editorial staff of Wallaces Farmer magazine since 1976, was appointed editor of the magazine in April 2003. He is widely recognized around the state, especially for his articles on crop production and soil conservation topics, and has won several writing awards, in addition to honors from farm, commodity and conservation organizations.

"As only the tenth person to hold the position of Wallaces Farmer editor in the past 100 years, I take seriously my responsibility to provide readers with timely articles useful to them in their farming operations," Rod says.

Raised on a farm that is still owned and operated by his family, Rod enjoys writing and interviewing farmers and others involved in agriculture, as well as planning and editing the magazine. You can also find Rod at other Farm Progress Company activities where he has responsibilities associated with the magazine, including hosting the Farm Progress Show, Farm Progress Hay Expo and the Iowa Master Farmer program.

A University of Illinois grad with a Bachelors of Science degree in agriculture (ag journalism major), Rod joined Wallaces Farmer after working several years in Washington D.C. as a writer for Farm Business Incorporated.

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